This invention relates to a magnetic recording and reproducing apparatus, and more particularly to a magnetic recording and reproducing apparatus to record an audio signal and a video signal which are superimposed on the same track of a magnetic tape by means of rotary heads to reproduce them therefrom.
At present, in the magnetic recording and reproducing apparatus of the helical scan system using a magnetic tape 1/2 inch wide, e.g., Video Tape Recorder (VTR), etc., rotary heads are mounted at positions opposite to each other on the rotating surface of the rotary body such as a rotary drum to run the magnetic tape obliquely wound over an angular range of, e.g., 180 degrees or slightly more onto the rotary body to record the video signal onto the magnetic tape by means of the rotary heads and to record the audio signal thereonto by means of a fixed head provided in the middle of the tape running path, and, at the time of playback or reproduction, to reproduce therefrom the video signal by means of the rotary heads and to reproduce therefrom the audio signal by means of the fixed head.
Further, there has been known such a VTR to superimpose the audio signal and the video signal on the same track formed on the tape and record them in order to effect high fidelity recording/reproducing of the audio signal.
However, in the case of attempting to record only the audio signal onto the tape by means of the rotary heads in the VTR (VTR I) adapted to effect recording/reproducing of the above-mentioned audio signal by means of the rotary heads, when the video signal has been input, this video signal was also recorded onto the tape as in the case of the ordinary recording, thus failing to record only the audio signal. Further, when the audio signal is reproduced after it has been recorded at the deep layer portion even if no video signal has been input, a single frequency-modulated carier signal such that it provides black level when reproduced would be recorded at the surface layer portion of the tape at the optimum recording level in that frequency, failing to record only the audio signal onto the tape.
On the other hand, in the case of attempting to record only the video signal onto the tape by means of the rotary heads, when recording is conducted with a VTR (VTR II) having only a function to effect recording/reproducing of the audio signal by means of the fixed head, only the video signal can be recorded onto the tape by means of the rotary heads.
Further, when there is employed a VTR (VTR III) provided with a switch for switching between execution and non-execution of recording of the audio signal by means of the rotary heads, this switch is used to make a switching such that, recording of the audio signal is not executed by means of the rotary heads, thereby making it possible to record only the video signal onto the tape by means of the rotary heads.
It is, however, to be noted that the rotary erasing head becomes operative in the same manner as at the time of the ordinary recording of the video signal and the audio signal, so signals recorded on the tape are erased by the rotary erasing head.
In the case of attempting to first record only the audio signal by the rotary heads using the conventional VTRs I, II and III thereafter to record the video signal onto the same magnetic tape by means of the rotary heads, for example, there is employed a method to use the above-mentioned VTR I to record only the audio signal by means of the rotary heads without inputting the video signal (a single frequency-modulated carrier signal such that it becomes black level when reproduced is also recorded), thereafter to use the above-mentioned VTR II to record the video signal by means of the rotary heads without erasing by the erasing head in the insert recording mode onto the track on which the previously-mentioned single frequency-modulated carrier signal is recorded such that it becomes black level when reproduced of the same magnetic tape in a manner that the video signal is superimposed on the single frequency-modulated carrier signal, thus making it possible to record only the audio signal by means of the rotary heads thereafter to record the video signal onto the same magnetic tape by means of the rotary heads.
For an alternative method of effecting such a recording as stated above, there may be employed an approach to first record only the audio signal by means of the rotary heads without inputting the video signal using the above-mentioned VTR I, thereafter to use the above-mentioned VTR III to make a switching of the switch so that recording of the audio signal by the rotary heads is not executed on the same magnetic tape, thus to record only the video signal onto the tape by means of the rotary heads.
In the case of the former method, there is no problem in connection with the audio signal recorded by means of the rotary heads, but there are problems of color moire and beat, etc. in connection with the video signal, because the video signal is recorded onto the track on which the single frequency-modulated carrier signal such that it becomes black level when reproduced is recorded, without erasing by the erasing head in the insert recording mode, in a manner that the video signal is superimposed on the single frequency-modulated carrier signal
In addition, in the case of the latter method, when recording is conducted using VTR III, the rotary erasing head becomes operative, so that the audio signal having been previously recorded by the rotary erasing head would be erased.
Anyway, when an attempt is made to first only the audio signal by means of the rotary heads thereafter to record the video signal onto the track on which the audio signal is recorded by means of the rotary heads in a manner that the video signal is superimposed on the audio signal, the audio signal and the video signal cannot be precisely recorded with the conventional VTRs.